Forming of a ceramic goods is generally carried out by a method such as wheel shaping, extrusion forming, injection forming, press forming, and sheet forming. However, because fluidity, shape retaining property, or the like which is necessary for the forming cannot be obtained if ceramics substrate powder alone is used, water, an organic binder, or the like is added to obtain a ceramics forming material and subsequently, forming is carried out. For example, a manufacturing method of a ceramic structure has been disclosed. According to this method, in the extrusion forming, a ceramics substrate, water, an organic binder, and the like are mixed, a forming material (clay) having improved formability is extrusion formed, and the clay thus extrusion formed is dried and fired (e.g., refer to Patent Document 1).
Formability of ceramics is improved if an additive amount of an organic binder or a surfactant which gives fluidity or shape retention property to a shaped body is increased. For example, to shape form a large-scale structure for DPF or a structure having a complex cell structure used for a water clarification apparatus, which has been increasingly in demand in recent years, by extrusion forming, a clay paste (clay) having superior formability to a clay used for manufacturing a small-sized or a simple-structured ceramic structure is required and as a result, it is inevitable to add more organic binder or surfactant.
However, if the additive amount of the organic binder becomes large, because the organic binder is burned in the firing, there is a problem that a space occupied by the organic binder in forming becomes a defect and mechanical strength of the structure is decreased. Moreover, in a large-scale structure, when the organic binder is burned in the firing, temperature inside the structure is elevated by the heat of combustion and due to thermal stress caused by difference in temperature between inside and outside of the structure, a defect such as a crack is generated. Not only does this lower mechanical strength of the structure, but this also significantly decreases yield. Further, CO2 or a toxic gas is generated by burning the organic binder in the firing and is released in the atmosphere, causing an environmental problem such as air pollution or global warming. Regarding the surfactant, it is true that the surfactant potentially has a basically same problem as that of the binder because the surfactant is also an organic.
Meanwhile, to ensure a desired porosity in a structure after firing which is a final product, especially in a large-scale structure for DPF or a structure having a complex cell structure used for a water clarification apparatus, it is necessary to use a larger amount of pore-forming agent in the substrate compared to a structure used for a general purpose. As a result, from a viewpoint of ensuring fluidity of a clay obtained by mixture, it is necessary to increase the amount of the organic binder, the surfactant, and water. However, if the amount of water added is increased to ensure fluidity, drying time is increased in a following drying step. Moreover, if the shape of the product becomes too large compared to a conventional product, moisture in the product is varied during drying and as a result a fine crack is partially generated during the drying to generate a problem such as triggering a crack in a final product. Therefore this is not preferable. In addition, in a case where the clay obtained by mixture includes much pore-forming agent, there is a problem that when a shaped body obtained by forming is calcinated for purpose of removing a binder, other organic such as the pore-forming agent is simultaneously removed and therefore strength of the calcinated body thus obtained tends to be low.
Meanwhile, clay as a substrate of a ceramic ware (potter's clay or the like) has a plasticity which enables forming even without including the above-mentioned organic binder. A factor for the clay to express the plasticity includes conditions such as a fine grain of the clay which has a flat or needle-like shape and generates hydrogen bond to water, and the like (refer to non-patent document 1). A compound having such characteristics is added to a ceramic substrate powder similarly to a conventional organic binder in a try to give plasticity to a ceramic substrate clay (refer to non-patent documents 2 and 3).
However, there is a problem that naturally produced bentonite, smectite, and the like disclosed in the above-mentioned non-patent documents 1 to 3 which are clay minerals having plasticity include lots of impurity and are expected to be depleted. Moreover, artificial ones or purified natural minerals are more expensive relatively to an organic binder.    Patent Document 1: Japanese Patent Publication No. 3227039    Non-patent Document 1: Nendo Handbook (Handbook on Clays) 2nd edition, (Gihodo Shuppan Co., Ltd. 1987)    Non-patent Document 2: Jinkou nendo (Artificial clay) (10th year anniversary issue of Jinkou nendo kenkyu-kai (Artificial clay study group))    Non-patent Document 3: The use of Montmorillonites as Extrusion Aids for Alumina, Ceram, Engi. Sci. Proc. 12 [1-2] pp. 33-48 (1991)